Question: Suppose the area of a circle is ${9\pi}$. What is its diameter?
${K = 9\pi}$ ${d = 6}$ First, find the radius: $K = \pi r^2$ , so $r = \sqrt{K / \pi} = \sqrt{{9\pi} / \pi} = {3}$ Now find the diameter: $d = 2r = 2\cdot {3} = {6}$.